Process and apparatus for waste liquid purification



PROCESS AND APPARATUS'FOR msm LIQUID PURIFICATIQN Filed April 5, 1955 Feb. 24, 1959 3 Sheets-Sheet 1 INVENTOR.

l MlLos KRor-'TA BY M Jj l @In AGENT Feb. 24, 1959 M, KRQFTA 2,874,842

PROCESS AND APPARATUS FOR rWASTE LIQUID PURFICATION Filed April 5 1955 l 5 sheets-sheet 2 Cl I C- 5 INVENTOR.

Y M LOS KROFTA "Y /M AGENT M. lKRol--TA v PRQCESS AND "APPARATUS FOR WASTE LIQUID PURIFICATION Filed April 5, `1955 .5 Sheets-Sheet 3 IN VENTOR MILOS KROF'I'A AGENT rby flotation.

l its separation.

United States Patent O vPRocn-ss AND APPARATUS non WASTE .LIQUID rmurrcArloN Milos Krofta, Lenox, Mass. Application April s, 195s, serial No. 499,326 14 claims. (ci. 21o- 70) This invention relates to the purilication of liquids containing suspended particles 'which can be removed The, invention pertains especially to the treatment of waste or rwhite watersof paper, cellulose, wood pulp and textile plants, in which waters the suspended particles are brought to the surface by means `of gas or air bubbles passing up through a body of the water.

The clarification of waste waters has been carried out in numeroustypes of apparatus and today the type frequently used relies on the principle of iioating the particles to the surface fof the `water and: mechanically Askimming the oat from the surface lof the water to eiec't However, all mechanical skimmers, whether radial blades on a rotating `:shaft for 'parallel slats on an endless conveyor, are `objectionable because 4they increase the cost of the vclarification equipment and 'thecost of'operation through lthe consumption `of power.

' An important object of this invention is to collect 'and remove the neat from a waste liquid undergoing purification without the use of mechanical skimmers Otherobjects and advantages of the inventionwill be apparent from the description which follows.`

`In accordance with this invention, the waste "liquid `containing suspended, *tioatable particles is treated with a gas so `that bubble`s`-rising through the liquid entrain the particles, "first alongincli-ned surfaces toward the periphery of the Vbody of liquid undergoing purification, and then along reversely inclined surfaces toward `a common point wherethe gas-entrainedllocs` are 'collected and removed; A distinctive 4and note-worthy 'feature of 'the invention is `the reverse tunnelI ilow fof the gasentrainedpartieles. That is `to say, the suspendedmatter maybe visualized as rising iii-st` along the exterior surfaceof an upright tunnel and then alongthe` interior surface of a superposed, inverted funnel;

To explain the invention further, reference 'will now be made to the accompanying drawings showing `several lillustrative forms of apparatusV embodyingrthe invertk Ytion. A

`Figure 1 is a Aschematic sectional elevation "of a white water purifier. Figure '2` is an enlargement fof the upper end of Figure l fand` Figure 3ds-a. plan viewlbased; on

Figure 2.

Figuresfl, 5, 6and `7` are schematic sectional` elevations -of four other forms oftwaste water purifiers.

In Figure l, cylindricall tank 1` -carries con'icall top 42` terminating` in generally cylindrical collar or- -stack '3 which has a slightgoutward taperin theupward direction. Tank lfissupported on!concreterfoundation 4 having aV lfloor` slightly pitched, toward sump` 5 at the `center of thetank. Duct'ti witha suitable valve is used to drain sump l5t Tube7; is disposed uprightoverfsump 5 with its lower end spaced therefrom. The upper-'end of tube, 7 is'tioinedgto` thre bot-tom -of` bowl-lile deflector 18,. l Baiiiei) taperingpoutwardlyin., thetupwarddirection is concentrically arrangedaroundttube 71 vRipe lfxpasses fhfqllltttalll liandldisuharsfsltllewhite wateninto theanl 2,874,842 Patented Feb. 24, 1959 ice nularfspace between'tube Tandbaie 9 Ri'ng11-closes the flower end of the annular space, s o that` the `*whitewater rises through this space and then flows r-adiallytoutwarlly 'below the bottom of dellector 8. Pipe 10 preterablyrenters baille 9 along a line tangent to the circle "midway between baffle 9 and tube 7 so that the whitewater will swirl up through the annular 'space 'within baiile 9.

Prior to entering the purifier, the white Water has `been treated under pressure inthe known manner with air, and ypossibly kwith a chemical, so as` to dissolve an 'ap preciable amount of air in the Waste water- Justfbe'fore entering the purifier, the white water undergoes a de'- crease in pressure with the result that shortly thereafter the dissolved air is released in the form `of t-iny bubbles. When the white water discharges into the puritier, these bubbles seek toV rise through the water and `form `the `entraining medium for carrying up the.` suspended `mfatter and effect-ing separation by llotatio'n.

ln Figure l, wavy line arrows indicate the general flow of the white water in the region where the bulk ofjthe 'air bubbles are being evolved, dash line arrows indicate the general flow) of the air-entrainedy particles, 'and smooth line arrows indicate the general flow of the puri- `lied water. Thus, the waste water with `evolving vaijr bubbles iiows up against the bottom of deiiector 8' which may be substantially flat in the central portion and 'curved upwardly in the outer portion to facilitate 'the` `upward migration of air-entrained particles., The rising particles accumulate at the `periphery "off tank 1 `and 'then Vreverse their flow by 'moving up along the inner surface 'of `conical top v`2 with the result" that the iioate'd matter is automatically 'brought to Aand `collected at the apex or 'cone "2i While the suspended particles move upwardly as de scribed, relatively clean water 'mig'rat'es `i-ntothe bottom of tank 1 and into the bottom offb'owlLlike reflector 8,. Upright tube 1'2 is disposed with itsrlovver end, spaced from the bottom "of bowl-like deector 8` and, its upper lend extending beyond the top of cone 2. vlferfora'ted plate 13 is placed along the bottom of tank` 1 around the lower end of 'tube 7 and a similar perforated plate 14 surrounds the lower end of tube 12 abo'vethe bottom of delieetor 8. APerforatedplate 1,3` ensuresmore even flow of clean water froml all` of the bottom` of tank 1 Vtoward withdrawal tube 7 and likewise ,perforatedplate 1 4 facilitates` desirable iiow of clean water from' the entire bottom of` deiiectorS towardwithdrawal tube `12. Clean water-flowing up` tube 7 continuesto Vrise-through tube 12, along with clarified-water colleotingin deliector 8 and entering thef'lower; end` oftube 12. Consequently, tube 12"has a larger diameter thanltube7t Therrelative proportions of clean waterwithdrawny at thevrbott'omof tank 1 and` atthe bottomI of deliector` 8? are1 controlled, respectively, byadjustable sleeves r15 and 16,itted inthe lower ends ofV tubes 7 and 1L When sleeves 15l and 16 areulowered sol thatuthey reston foundation 4l` and de ector 8, respectively, the How of water to tubes 7 and 12 is stopped Conversely,` iiow occurs when` either sleeve is .raised and maximum flow takesr place when the bottom` edge oft` the sleevelno longer projectsoutbf thelower end of the tube in which; the sleeve dis'- posed lAdjustrrlent of sleeves 15 -andlmay beachieved by means offrods .17 and 18respectively, extending to the topof the purifier whereone may pull them up or `drop `t`hem as-desired- Rodslfl andflS-are shownonly. .partially to prevent obscurementof more essential, parts of the apparatus.` Eachtrodli's attached totthe insd'eo'f its sleeve by a suitable. bracket or,` spider (notl shown) andl at` least one of. the two rods is: 'eccentrieally posi tioned so that the two rods donut` interfere withone another. Rodi17: passes;` up `throughr the hollowlp'art ofsleeve 16 so that sleeve 15 may be adjusted without disturbing sleeve 16.

The upper end of tube 12 has a semi-circular cut-out so that the clarified water in tube 12 spills over the cutout edge 19 into stack 3. The details of the top of the purifier are shown in Figures 2 and 3.

The annular space between stack 3 and tube 12 is divided by two vertical baffles 20 and 21 extending from the top of tube 12 to the level of cut-out edge 19. A pair of curved batlies 22 and 23 are joined to the bottom edges of baffles 20 and 21, respectively, and slope downwardly Vtoward the bottom of stack 3 where the two bafiies 22 and 23 are joined together along line Z4.

yWith this construction the clarified water flowing up tube 12 spills over cut-out edge 19, runs down curved baflles 22 and 23, and discharges from the annular space between stack 3 and tube 12 through outlet 25.

Stack 3 is also provided with outlet 26 on the side opposite that of outlet 25. A pair of curved batiles 27 and 28 are joined together along line 29 just below outlet 26 and extend upwardly through the annular space between stack 3 and tube 12 but do not reach and connect with vertical bafes 20 and 21 as do curved baffles 22 and 23. Rather, bafiles 27 and 28 terminate some distance from vertical bafiles 20 and 21, respectively. The upper edges of bafhes 27 and 28 are connected with the lower edges of vertical bafiics 30 and 31, respectively, the upper edges of which are on the same level as cutout edge 19. The floated particles collecting at the top of cone 2 move up along the bottom surfaces of curved .bafiies 22, 23, 27 and 28, spill over vertical bai-lies 30 and 31, run down the upper surfaces of curved baies 27 and 28, and discharge through outlet 26.

Since the fioat passing over baiiies 30 and 31 has a lower hydraulic resistance to flow than the clarified water flowing up tube 12 and over cut-out edge v19, it is generally advisable to equalize the hydraulic heads of the two overflowing liquids by raising the level of the fioat slightly above'that of the clean water. As shown in Figure 3, this may be done with adjustable Weir plates 32 and 33 contiguous to bafes 30 and 31, respectively. Usually, Weir plates 32 and 33 are raised so that the oat owing over them has a level approximately one inch higher than that of the clean water spilling over cutout edge 19.

Heavy particles settling out of the waste water and collecti-ng at the bottom of bowl-like defiector 8 and tank 1 are periodically flushed out of the purifier through sump 5 and duct 6.

The purifier of Figure 4 is much like that of Figure 1 except that internal tube 12 of Figure l for the withdrawal of clean water has been replaced in Figure 4 with extemal'tube 40. Clean water leaves the bottom of the Vpurifier through duct 41 provided with a butterfly valve 42 to regulate the flow while clean water passes from bowl-like deector 43, down tube 44 and through duct 45 which has ow control valve 46. Ducts 41 and 45 discharge into tube 40. Valved drain 47 is occasionally used to ush out heavy particles settling in the purifier. In this illustration, to make the level of the lioat at the top of the purifier higher than that of the water in tube 40, an adjustable weir sleeve 43 is fitted in the upper end of tube 40. The water spilling over the top edge of Weir sleeve 48 has a slightly lower level than that overowing the top of cone 49 into stack 50. The float issues from stack 50 through outlet 51 while the clarified water spilling over weir sleeve 48 leaves basin 52 through outlet 53. In other respects, the purifier of Figure 4 is essentially like that of Figure l, the white water and `entraining air being introduced through pipe 54 and cylindrical baffle 55 disposed around tube 44.

Figure 5 shows a purifier forV operation at subatrnospheric pressure, Tank is set on an upper floor of a building and withdrawal tubes 61, 62 and 63 extend downwardly to a vlower floor, acting as barometric legs 4 to reduce the pressure in the purifier and thus facilitate the evolution of air bubbles in the white water. Clear water leaves tank 60 through tube 61 and bowl-like deector 64 through tube 62, while the concentrated suspension of air-entrained particles fiows from stack 65 through tube 63 into reclaimed stock tank 66. White water is pumped into feed tank 67 and thence passes up pipes 68 and 69 into the annular space between tube 62 and cylindrical baffle 70. Whereas the purifiers described hereinbefore are open at the top to the atmosphere, the purifier of Figure 5 has a seal cap 71 mounted on stack 65 to permit operation at reduced pressure. Excessive accumulation of gas in stack 65 is prevented by float 72 which operates to open valve 73 in gas vent pipe 74 when too much gas begins'to collect in stack 65. Pipe '74 is connected to an air suction pump (not shown).

The withdrawal of clean water from bowl-like deflector 64 is controlled by damper 75 in tube 62, while similar control means 76 in the annular space between tubes 61 and 62 regulates the flow of clean water from the bottom of tank 60 by way of tube 61. All of the clean water passes from the lower end of tube 61 into seal tank 77 and discharges from outlet 78.

The purifier of Figure 6 has two stages for carrying out the reverse funnel fiow principle of this invention. Gas-entraiued particles rising from the waste liquid introduced into the bottom of tank 80 by way of pipe .81 move outwardly along the bottom surface of bowllike defiector 82, then inwardly up the internal cone 83, again outwardly along the bottom surface of deilector ,84, and finally inwardly up cone where the collection of the suspended particles is completed. ln the meantime, clarified liquid ows from the bottom of tank 80 up tube 86, from within deflector 82 up tube 87, from the space between cone 83 and deflector 84 through a plurality of radially arranged tubes 88, and from Within deflector 84 up tube 89. All of the clarified liquid discharges from the upper end of tube 89 as already explained in connection with Figure 1. The float collecting in the top of cone 85 is also withdrawn as described for the apparatus of Figure 1. Forany given horizontal cross-sectional area, the two-stage purifier of Figure 6 will handle approximately twice as much Waste liquid as will the single-stage purifier of Figure 1.

Another type of multi-stage purifier is shown in Figure 7. The white water is supplied from manifold pipe 90 through valved pipes 91, 92 and 93 to distributor cups 94, and 96, respectively. Clarified water flows from the bottom of tank 97 into tube 98, from within defiector 99 into tube 100, from within defiector 101 into tube 102, and from within deector 103 into tube 104. Air-suspended flocs move outwardly beneath defiectors 99, 101 and 103, up the walls of tank 97 and into collecting cone 105. The rate at which white water enters each level of the purifier is independently regulated and it is generally advisable to have about the same rate at every level of entry. The withdrawal of clear water and concentrated stock from the top of this purifier is the same as that described in connection with Figure 1. For any given diameter, the multi-stage apparatus of Figure 7, like that of Figure 6, will clarify more gallons of waste water per minute than will the single-stage unit of Figure 1. A multi-stage purifier with several vertically spaced inlets for the white water as shown in Figure 7 will generally ensure more uniform dispersion of small gas bubbles and, therefore, better clarification of the water through flotation than a multi-stage unit with a single bottom inlet as shown in Figure 6 where the bubbles tend to enlarge as they rise through the water and become less eflicient in the entrainment of suspended particles. l

The purifying apparatus of this invention is provided with a slanted top which extends from the periphery of the tank portion of the apparatus upwardly toward an opening for the discharge ofthe floated particles. It

aafzagsaa lcharged. .'llhe :outer or `peripheral `portions tof `the bowlf .like ='deflector"s, as `well as rinternal slanted `baffles like Ibafile 8 3 lof FigureA 6, `should -also be disposed at an angle .in the range horizontal.

"While in most instances, the entraining gas, usual-1y air,` used to float the suspended particles `inthe waste liquid, is dissolved under pressure in the liquid prior "to `its introduction "into the purifying apparatus of this' in- `vention, it is also possible to bubblesuch` 4gas directly Vinto the apparatus `in the vicinity in which the WaSe liquidis introduced. Also, chemical assistants, such' as `coagulating and lluocculating agents, may be. added `to `the waste .liquid either `before it is introduced 'intothe .purifying apparatus or ldirectly in the `apparatus in `the region which the waste liquid fis introduced.

To illustrate the invention further, in a specific eX- ample ofapparatus asshown in Figure l., @cylindrical tank 12.5 feet .in 4diameter. and 5 feet, height, and having a conical" 'top making a 45 angle lwith the hori- Vzloutah is capable-of purifying 500 gallons of white water minute; The fiber suspended in'the whitefwater amounts 5to `8 `pounds per thousand gallons. The clari- Afied water withdrawn from `the `apparatus contains .not `more than `f0.5 `pound of fiber per thousand gallons and fthe floated fibers discharge `from the conical `top ofthe fapparatusas a suspension in onlyV 5% #of the white water introduced into the apparatus. ."lvhis amount of concentration of the fioa'tediibers is noteworthy in view of curfnent practicefwhere the concentrated `fibers are discharged as a suspension involving about 2S to 30% of the waste liquid undergoing purification.

It is well to note that the single-stage purifiers of Figures 1, 4 and 5 involve two superposed, separation zones in which the suspended particles are concentrated by flotation. In the purifier of Figure l, one separation zone is at a level approximately midway between floor 4 and the bottom of deflector 8, and the other separation zone is approximately at the level where conical top 2 meets cylindrical tank 1. Generally, each of the two separation zones effects clarification of approximately one-half of the waste liquid entering the purifier. Thus, 40 to 60% of the clarified liquid will be drawn from the bottom of tank 1 and the remaining portion from within bowl-like defiector 3. The waste liquid clarifying capacity of the apparatus is proportioned to the sum of the horizontal cross-sectional areas of the two separation zones. In a typical case, each square foot of horizontal separation area will handle approximately 2.5 gallons of waste liquid per minute.

The height of the tank portion of the purifier is primarily dictated by bafe 9, which is usually 2 to 4 feet in height, and the depth of bowl-like defiector 8 which is dependent on `its diameter and a sufficient slant or curvature to facilitate outward movement of the gasentrained flocs along the bottom surface of the deflector. The annular clearance between the edge of deflector 8 and tank 1 is generally 2 to 4 inches. While cylindrical tanks and conical tops are frequently preferred, other shapes may be used. Thus, the tank may be rectangular in horizontal cross-section and the top may be quasipyramidal. Also, the upward slant of the top may have curvature, that is, the top may be dome-like.

The degree'of concentration of the oated particles which can be achieved is related to, and controlled by, the sizes of the openings through which the clarified liquid and the float are discharged. In an illustrative case, referring to Figures 2 and 3, eut-out edge 19 for the discharge of purified water is 27 inches wide and batiles 30 and 31 for the discharge of the float are each 6 inches wide. While a high degree of concentraof 30 toto? with Vrespect `to the a .tion @inthe floatedpartiles its obtained ,with the foregoin's ratio, of' 2.17` to`12 forth@ widths of Tthe overflow openings for the purified water and the foat Arespective-.15p this `ratio .may be readily adjusted as desired .For insta-nce., 01 a still higher .degree of concentration,

`the uppen part `o f weir-plates` ,32 ,and 33 Vcontiguous to `baffles. 30` and 31. respectively. may be notched out so `that when these -weir plates are .raised the original width 01E-6 inches 4for -each lloat2 overflow isl decreased to,

sav. v4 inches.

ln 'View of the various modifications of fthe invention which will occur to those skilled in the `art upon consideration of the foregoing disclosure withoutdeparting `from -the spirit or `scope thereof, only` -such limitations should Vbe imposed as arie indicated by. the appended claims.

Whajt `is claimed is:

l. In the puritiication ofliquids containing suspended particles by flotation of said (particles, fthe improvement which` comprises introducing'a liquid :containing suspended particles and. pressurized gas` into 4the lower central portion of a body 0f `said `liquid while releasing .in said iliquid said gas in the form, of .small bubbles to entrain said particles .to the `top, `of `said body` of said liquid, deflecting the Vflow. `of the :gas-entrained particles `in `said Alower central kportion :laterally in `substantially all directions toward the peripheral portionof said body `-o'f said liquid, thence defiecting .the flow yof said gas-entrained particles upwardly in .inclined directions toward t a common :point'of withdrawal, and withdrawing purified liquid fromthe bottom of `said body` of said liquid and from a higher level in said body .of said liquid- `above lthe level where theiiow-of said .gas-entrained particles is rdeflected `tojwards'aid Cperipheral vportionof `said .bodyof fsaid. liquid.

2. The process of claim 1 wherein the purified liquid withdrawn from the bottom of said body of said liquid is not more than 60% by volume of the total purified liquid. Y

3. The process of claim l wherein the inclined directions are at an angle of about 30 to 60 to the horizontal.

4. Apparatus for purifying liquids containing suspended particles by flotation of said particles comprising a tank, a bowl-shaped deflector in said tank disposed with its convex surface in spaced relation to the bottom of said tank, means for introducing a liquid containing suspended particles and an entraining gas into said tank below said convex surface of said defiector, a slanted top on said tank extending from the periphery of said tank upwardly toward an opening for the discharge of floated particles, and means for withdrawing purified liquid from the bottom' of said tank and from within said deflector.

5. The apparatus of claim 4 wherein the tank is cylindrical and the slanted top is a cone forming with the horizontal an angle in the range of 30" to 60.

6. The apparatus of claim 4 wherein the means for withdrawing purified liquid from the bottom of said tank comprises a tube in communication with said bottom and extending upwardly through the bowl-shaped deliector.

7. The apparatus of claim 6 wherein the means for introducing the liquid comprises an upwardly open cup disposed below the bowl-shaped deliector and around the tube extending upwardly through said deflector, and a pipe for discharging said liquid into the lower portion of said cup.

8. The apparatus of claim 4 wherein the means for withdrawing purified liquid from the bottom of the tank and from within the bowl-shaped defiector comprises a vertical tube with its lower end in communication with said bottom and its upper end forming a funnel-shaped structure with said deflector, and a second vertical tube with its lower end in communication with liquid in said deflector and its upper end projecting through the slanted top.

9. Apparatus for purifying` liquids containing suspended particles comprising a tank, a series of vertically spaced bowl-shaped deectors in said tank disposed with their convex surfaces facing downwardly and with the lowermost convex surface in spaced relation to the bottom of said tank, means for introducing a liquid containing suspended particles and an entraining gas into said tank below said lowermost convex surface, a slanted top on said tank extending from the periphery of said tank upwardly toward an opening for the discharge of oated particles, and means for withdrawing purified liquid from the bottom of said tank and from within each of said deectors.

10. The apparatus of claim 8 wherein the means for withdrawing puried liquid from the bottom of said tank comprises a tube in communication with said bottom and extending upwardly through the lowermost bowl-shaped deftector, and the means for withdrawing purified liquid from the uppermost bowl-shaped decctor comprises a second tube in communication with the lower portion of said uppermost bowl-shaped deector and extending upwardly through the slanted top.

11. The apparatus of claim 9 wherein a slanted balle is disposed in the space between two succeeding deectors, said baille extending from the periphery of the tank upwardly toward an opening adjacent the bottom of the higher of said two succeeding defiectors.

12. The apparatus of claim 9 wherein means for introducing an additional quantity of said liquid and entraining gas is disposed to discharge said liquid and entraining gas below one of the deectors other than the lowermost deector.

13. A process for purifying liquids containing suspended particles by flotation of said particles, which comprises introducing a liquid containing suspended particles and small gas bubbles into the central portion of a mass of said liquid having an appreciable horizontal cross-sectional area for otation separation, withdrawing a rst purified portion of said liquid from the bottom portion of said mass, owing another portion of said liquid with gas-entrained particles from said central portion of said mass radially upward to substantially all of the top peripheral portion of said mass'and thence into substantially all of the bottom peripheral portion of a superposed mass of said liquid having an appreciable horizontal cross-sectional area for flotation separation, directing said gas-entrained particles from said bottom peripheral portion radially upward to the top portion of said superposed mass, withdrawing a second puried portion of said liquid from the central bottom portion of said superposed mass, and withdrawing said gas-entrained particles from said top portion of said superposed mass.

14. The process of claim 13 wherein the rst and second purified portions of said liquid are each in the range of 40to 60% by volume of the total puried liquid.

References Cited in the tile of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No., 2,874,842 February 24, 1959 Milos Krofta It is hereb17 certified that error appears in the -printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 71, line I4, for the Claim reference numeral "8" read -1- 9 `Signed and Sealed this 23rd day of June 1959.

(SEAL) Attest:

KARL AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents 

